The present invention relates to a gear arrangement for a development unit of an imaging device employing an electrophotographic process.
Conventionally, gears are arranged such that an input gear coupled with a rotation member provided to the development unit meshes with a drive gear provided to the imaging device such that the development unit is swingably supported by the main body of the imaging device through a support shaft and mounted to a predetermined position of the main body, and the rotation of the drive gear is transmitted to the input gear to thereby rotate the rotation member.
Conventionally known are imaging devices such as an electronic copy machine, laser beam printer and the like which make use of the electrophotographic process.
Although various systems can be contemplated to develop images in the electrophotographic process, a system referred to as a magnetic brush method is generally employed, wherein charged toner is supplied to an electrostatic latent image by a magnetic material carrier (magnetic brush) arranged as a chain by a magnet.
The magnetic brush method employs a two-component developer composed of non-magnetic toner mixed with a magnetic material carrier at a preset ratio. Recently, however, a system of using a single-component charged type magnetic toner and a development roller to which a magnetic material carrier is predeposited is also employed by the method.
A development unit to which the aforesaid magnetic brush method is applied is provided with a development roller which is composed of a magnetic roller and a sleeve of a non-magnetic material rotatably inserted around the periphery of the magnetic roller, and toner is sequentially supplied to a development area by the rotation of the sleeve of the development roller.
To stably perform a development operation by the arrangement described above, a gap (development gap) between the circumferential surface of the development roller and the circumferential surface of a photoconductive drum must be set with a pinpoint accuracy. For this purpose, conventionally, guide rollers each having a radius obtained by adding the development gap to be set to the radius of the development roller are rotatably disposed on the opposite ends of the development roller, and the development gap is set at a pinpoint accuracy by causing the guide rollers to be abutted against the circumferential surface of the photoconductive drum. The development unit is swingably mounted to the main body of an imaging unit through a support shaft, so that it can be moved in the direction along which the development roller approaches and retracts from the photoconductive drum.
A rotating force, for rotating the development roller, is transmitted in such a manner that an input gear coupled with the development roller meshes with the drive gear provided to the main body of the imaging device, so that the development unit is set at a predetermined position with respect to the main body of the imaging device. A drive force transmission mechanism composed of the input gear and drive gear need only be provided at one end of the development unit, from the view point of the function thereof.
Nevertheless, with the above arrangement, a problem arises in that the development unit is swung by the rotational torque of the drive gear, and when the drive force transmission mechanism is provided on only one end of the development unit, an urging force for pressing the development roller against the photoconductive drum (i.e., a pressing force for causing the guide rollers to be abutted against the circumferential surface of the photoconductive drum) is slightly different between the right end and the left end of the photoconductive drum. Thus a recording paper is irregularly developed in the width direction of the paper.
This problem can be solved by providing drive force transmission mechanism at both the right and left ends of the development roller (providing drive gears and input gears at the opposite ends) so that a change in a force for pressing the development roller caused by a drive torque being transmitted is made uniform on the right and left sides of the development roller. In this case, however, cost is increased because the structure is made to be more complex. Further, a change in the force for pressing the development roller against the photoconductive drum is not desirable, even if the force is uniformly changed at the right and left ends of the development roller.